This disclosure relates to a self-drilling and self-tapping bone screw, and in particular to self-drilling, self-tapping, fully cannulated fenestrated and non-fenestrated bone screws, and even more particularly to such self-drilling, self-tapping pedicle screws. This disclosure further relates to methods of installing such bone screws in a variety of surgeries including, but not limited to spine surgery. However, the methods of this disclosure will be described for use with spine surgeries and more specifically in regard to installation of pedicle screws in the sacrum, but those skilled in the art will recognize that the self-drilling, self-tapping bone screws of the present disclosure may be used a wide variety of applications, including trauma and reconstructive bone surgery. The fenestrated embodiments of the self-drilling, self-tapping bone screws of the present disclosure may be used in conjunction with a method of injecting bone cement into the bone structure into which the bone screw is inserted so as to stabilize the bone structure and to increase the purchase of the bone screw in bone structure having diminished or osteoporotic bone quality, such as described in my U.S. patent application Ser. No. 14/148,207, which is incorporated by reference herein.
Posterior pedicle screws have long been used in spine surgery. Such pedicle screws have been used with rods and other constructs in spine surgery. In cases where the pedicle screws are placed in the sacrum, such constructs have been known to fail distally at the sacrum because the cancellous bone of the sacrum is significantly weaker than lumbar vertebrae body bone. With reference to the sacrum, there is an anterior avascular “safe” zone in the presacral space where major arteries and veins are not present and therefore allow for bicortical or even tricortical purchase of pedicle screws in the sacrum, even where the distal end of the screw extends slightly into this presacral space. However, because in minimally invasive surgical (MIS) techniques the placement of such pedicle screws in the sacrum is typically performed over a guide wire and cannulated pedicle screws are blunt tipped, it is not possible to achieve such bicortical purchase of the screws in the sacrum.
In open techniques to achieve bicortical purchase, the surgeon drills a pilot hole through the entire bone structure before tapping and inserting the bone screw. In percutaneous MIS surgery techniques prior art cannulated pedicle screws are typically blunt tipped, non-self-drilling screws. Additionally a pilot hole cannot be drilled through the distal anterior cortical bone margin without risking the sharp tipped guide wire perforating organs in the pelvis. Consequently a blunt tipped cannulated pedicle screw encountering a distal cortical margin that had not been perforated with a pilot hole would spin in place, not advance, and the threads formed by the self-tapping screw in the more proximal cancellous bone. Consequently the surgeon has to settle for unicortical fixation which is inherently weaker than the bicortical purchase of open techniques.
In open spinal surgical techniques that are intended to achieve bicortical purchase in the sacrum (or other bone structure), the surgeon drills a pilot hole through the entire bone structure, and then taps the pilot hole before inserting the bone screw.